Conventional optical position-measuring devices usually include a measuring graduation as well as a scanning unit, which is movable relative thereto in the measuring direction. On the side of the scanning unit, there is generally a light source, collimator optics, one or a plurality of scanning graduations as well as one or a plurality of opto-electronic detector elements. The position-measuring devices, in particular the scanning unit, are often required to be as compact as possible. These requirements can be fulfilled by guiding the scanning beam in an appropriate manner. In particular, folded scanning beam paths are advantageous, which, in addition to the components described above, further include one or a plurality of deflector or reflector elements disposed on the side of the scanning unit.
German Patent 26 15 676 describes an optical position-measuring device having a folded scanning beam path. The collimator optics and a deflector element are integrated in a single optical component. The component having the optical double function in the scanning beam path can be a mirror lens. However, details of the mirror lens, in particular with respect to its manufacture, are not described in this patent. According to this patent, the proposed mirror lens provides deflection and collimation of the beams of light, but has a relatively large unit volume. Also, due to the proposed optical path in the mirror lens, light cannot be prevented from reaching the collimator optics directly from the light source, without any previous deflection of these beams of rays. Consequently, a desired pupil separation is not guaranteed when using this component for folding the scanning beam path.
A similar mirror lens in the folded scanning beam path of an optical position-measuring device is also known from German Patent 36 09 211 A1. A disadvantage of this design of a mirror lens is// that two reflector surfaces are required to produce the desired deflection. However, highly exact reflector surfaces require a considerable effort during manufacture, similar to the manufacture of two spatially separated, curved lens surfaces via which the scanning beam enters and exits.
The present invention is an optical position-measuring device which includes a scanning unit having a compact design. The optical components in the scanning beam path ensure a good signal quality of the resulting scanning signals, and also can be manufactured in a simple manner.
In one embodiment, the invention is an optical position-measuring device having a scale and a scanning unit movable relative thereto, comprising a light source, a plurality of scanning graduations, at least one opto-electronic detector element, a mirror lens disposed downstream of the light source, and a single plane reflector surface formed on the mirror lens. The invention also includes a first and a second partial surface portion of the mirror lens, the first partial surface portion having a different curvature than the second partial surface, disposed opposite of the single plane reflector surface such that beams of light entering the mirror lens through the first partial surface portion impinge on the reflector surface and are reflected towards the second partial surface portion. The curvatures of the first and second partial surface portions are selected such that a collimated beam of light exits the second partial surface area, and that optical axes of the first and second partial surface portions intersect one another in a plane of the reflector surface.
According to an embodiment of the present invention, the scanning unit includes a mirror lens which, in addition to the optical collimation effect, allows the scanning beam path to be deflected or folded. The exemplary mirror lens has only a single plane reflector surface, opposite of which two partial surface areas having differently curved surfaces are arranged. In each case, one optically active partial surface area is allocated to the incident beams, and the other to the emergent beams. The different partial surface areas are preferably designed as optically active or imaging asphere, which results in a larger usable image field angle.
Due to the folding of the scanning beam path according to the present invention, the desired compact design of the optical position-measuring device is obtained. The mirror lens required for this design is easy to manufacture, which results from the approximated piano-convex shape of the mirror lens which ensures a simple moldability of the two partial areas having different optical properties. The mirror lens can be manufactured both from glass or from plastic. The mirror lens is preferably manufactured by one-sided glass pressing, i.e., the convex side of the mirror lens having the two differently curved partial areas is pressed, whereas the plane side having the reflector surface is polished. During manufacture, it is thus possible to form the reflecting plane surface markedly more precisely, or truer in shape, than the convex lens surface.
The design of the mirror lens also guarantees a good quality of the scanning beam, in particular a good collimation of the beam.
Further advantages and details of the present invention are revealed by the following description of an exemplary embodiment of an optical position-measuring device, on the basis of the enclosed drawings.